1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and a mask used to form a thin film pattern.
2. Description of the Related Art
A semiconductor light-emitting element (LED) is generally used which includes an N-type GaP layer and a P-type Gap layer stacked in order on a semiconductor, e.g. GaP substrate and an electrode of e. g. Au formed on the P-type GaP layer. Such a semiconductor light-emitting element can be manufactured as follows. First, a semiconductor wafer (hereinafter also referred to as "semiconductor substrate") is prepared by stacking the N-type GaP layer and P-type GaP layer in order on the surface of the GaP substrate. In this state, electrodes each having a prescribed diameter are arranged at a prescribed pitch on the front surface of the semiconductor substrate on the side of the P-type GaP layer. Electrodes are also arranged on the back surface of the semiconductor substrate. The semiconductor substrate is diced into plural pieces each having a single (P-type) electrode on the front surface and plural electrodes on the back surface. The electrodes are formed with a mask having through-holes mounted on the semiconductor substrate within a metallic vacuum.
FIG. 21 shows a schematic configuration of a vacuum deposition apparatus for forming electrodes. Within a bell jar (deposition vessel) with an evaporation source such as a pot arranged at a predetermined position, a fixed stand 3 is arranged so that it can swing within a prescribed angle with respect to the deposition source 2. A semiconductor substrate 4 and a metallic mask 5 are mounted on the fixed stand 3. The evaporated metal having flied from the evaporation source is deposited on the surface of the semiconductor substrate 4 exposed within through-holes. In the above process, the semiconductor substrate 4 is placed on the fixed stand 3 and the metallic mask 5 having a diameter equal to that of the semiconductor substrate and through-holes each having a prescribed shape made at a prescribed pitch is arranged on the semiconductor substrate 4. Using pins or the like, the metallic mask 5 and semiconductor substrate 4 are fixed on the fixed stand 3 at plural positions in the vicinity of the edge of the metallic mask 5. Although not shown, a spacer is arranged between the metallic mask 5 and semiconductor substrate 4 as occasion demands.
In this state, when the evaporation source 2 is heated, metallic atoms 7 evaporated from the evaporation source 2 fly toward the metallic mask 5. As seen from FIG. 22 which is a partially enlarged sectional view of the metallic mask 5 and semiconductor substrate 4, the metallic atoms are deposited on the semiconductor substrate 4 through through-holes 8 made in the metallic mask 5. Thus, the electrodes 9 each having a prescribed shape are formed at a prescribed pitch on the semiconductor substrate 4.
In the case of the LED element, each of the through-holes 8 of the metallic mask 5 corresponds to the electrode of each LED element. In the case of an IC, a plurality of electrodes are often formed on a single chip. In this case, several through-holes of the metallic mask 5 are formed within a single IC element so as to correspond to its electrodes.
The metallic mask 5 is as thin as several tens of .mu.m so that it expands owing to heat from the evaporation source 2. Thus, it becomes deformed in various shapes, for example, its central portion swells. If the metallic mask 5 becomes deformed, the semiconductor substrate 4 may be greatly separated from the metallic mask 5 and the locations of the through-holes of the metallic mask 5 may vary momently. Therefore, it is difficult to form electrodes precisely so that they are located at prescribed positions so as to have prescribed shapes.
During the deposition, the metallic mask 5 is liable to suffer from heat. The metallic mask 5, which has a larger thermal expansion coefficient than that of the semiconductor substrate 4, is apt to expand. If it has a large size to provide a wide free region, it is more likely to become deformed. In order to minimize such a deformation of the metallic mask 5, the metallic mask 5 is commonly formed to have a size equal to that of the semiconductor substrate 4 Therefore, when the metallic mask 5 is fixed, in alignment with the semiconductor substrate 4, on the fixed stand 3, the fixing pins 6 are also located on the semiconductor substrate 4. Thus, no deposition is made on the surface of the semiconductor substrate 4 where the pins 6 are located. This leads to reduction in the production yield in the electrodes. The present invention has been accomplished in order to solve the problem described above.